1. Field of the Invention
This invention relates to a self-averaging pitot tube probe and method for measuring fluid flow, and more particularly to a self-averaging pitot tube probe and method for use with a measuring device for measuring a pressure differential to determine fluid flow rate in a conduit, wherein the probe and method provide a stable and more accurate sensing of the low pressure component of the pressure differential and, thus, a higher degree of accuracy in the measurement of the fluid flow rate.
2. Description of the Related Art
U.S. Pat. No. 3,581,565 to P. D. Dieterich discloses a pitot tube flow measuring device comprising an upstream probe including an elongated hollow cylindrical body of circular cross section, which extends diametrically across a pipe or conduit during a flow measuring operation. The hollow cylindrical body has a plurality of longitudinally arranged high (dynamic) pressure sensing ports at an upstream side of the body. An interpolating or averaging tube is located within the hollow cylindrical body and has, at one end, an open port located centrally of the body for determining an average of the fluid flow into the body through the upstream sensing ports. The flow measuring device further includes a downstream probe of circular cross section and cylindrical construction, with a downstream facing port located centrally of the conduit in a low (static) pressure area. Both of the upstream and downstream probes are connected to a pressure differential measuring mechanism mounted externally of the conduit.
Another pitot tube flow measuring device, which is intended to be an improvement over the flow measuring device disclosed in the above-mentioned Dieterich patent, is disclosed in U.S. Pat. No. 4,154,100 to J. B. Harbaugh et al. This flow measuring device comprises a probe including an elongated hollow body having a portion of its length of triangular or diamond-shaped cross section, rather than circular. A key feature of the probe is the provision of sharply contoured edges located in transversely-spaced relationship on opposite sides of the hollow body, intermediate upstream and downstream facing surfaces.
More specifically, the upstream-facing surface is contoured to divide the fluid flow and direct essentially equal parts thereof across the sharply contoured opposite side edges, which function to fix the locations at which fluid flow boundary layer separation from the body occurs over a broad range of laminar and turbulent flow conditions. The downstream-facing surface is shaped so that reattachment of the fluid to the body then is precluded and so that a low (static) pressure sensing port in the downstream-facing surface lies within the wake of the fluid flowing past the sharply contoured edges, in a low (static) pressure area. The probe also includes upstream high pressure sensing ports and an internal interpolating or averaging tube, as in the flow measuring device of the above-mentioned Dieterich patent, and further includes an internal low pressure sensing tube, one end of which defines the above-mentioned low pressure sensing port in the downstream-facing surface of the probe body.
The primary purpose of this invention is to provide a new and improved self-averaging pitot tube probe and method for use in a measuring device for measuring a pressure differential to determine a fluid flow rate in a conduit, such as disclosed in the Dieterich and Harbaugh et al patents, wherein the probe provides a stable and more accurate sensing of the low pressure component of the pressure differential, and thus provides a higher degree of accuracy in measuring the fluid flow rate.